The disclosures herein relate generally to thermally conductive interface members. More particularly, the disclosures herein relate to thermally conductive interface members for heat generating components in a computer system.
Heat dissipating devices are commonly used to aid in dissipating heat from heat generating components in electronic devices such as computers. The performance and operating life of heat generating components are adversely affected by excessive temperatures. Heat dissipating devices are configured to readily dissipate heat from one or more heat generating components to the surrounding atmosphere. To provide for acceptable and efficient heat transfer, the heat dissipating device must be in sufficient contact with the heat generating component.
In a portable computer, the use of a heat dissipating device to control the operating temperature of the microprocessor is essential. Furthermore, maintaining a suitable thermal interface between the microprocessor and the heat dissipating device is extremely critical. If the microprocessor temperature is not kept within the specification limits of the component, the effective life and performance of the microprocessor will be greatly diminished. Minimizing the thermal resistance between the microprocessor and the heat dissipating device greatly improves cooling efficiency.
U.S. Pat. No. 5,738,936 discloses a thermally conductive article including a polytetrafluoroethylene matrix, an elastomer interpenetrating the polytetrafluoroethylene matrix, thermally conductive particles and expanded polymeric particles. The thermally conductive article is compressible.
U.S. Pat. No. 5,060,114 discloses a conformable, gel-like pad with a thermally conductive additive that conducts heat away from a packaged electronic power device to with which it is in contact. The pad includes particles of a thermally conductive material such as aluminum, nickel, aluminum oxide, iron oxide, beryllium oxide, or silver. A thin, solid sheet of a thermally conductive metal such as aluminum, positioned in contact with a surface of the conformable pad, further increases heat removal.
U.S. Pat. No. 5,184,211 discloses a packaging and cooling assembly for semiconductor devices. The assembly includes a base for receiving one or more semiconductor devices and a combination heat sink and cover for attachment to the base. Compliant cushions that generally conform to the shape and size of the semiconductor devices are held loosely between the circuit sides of the semiconductor devices and the base. The heat sink engages the back sides of the semiconductor devices when it is attached to the base, causing the semiconductor devices to compress the compliant cushions and hold the semiconductor devices firmly in position. In this manner, a low resistance thermal interface is established between the semiconductor devices and the heat sink. To further enhance the heat transfer characteristics of the interface, a thin film of fluid is coated on the back sides of each semiconductor device to fill in the microvoids which result from uneven contact of the heat sink and semiconductor device mating surfaces.
U.S. Pat. No. 4,233,645 discloses a semiconductor device package having a substrate, one or more semiconductor devices mounted on a top surface of the substrate, and a heat sink having a surface in opposed spaced parallel relation to the top surface of the substrate. At least one deformable heat transfer member is positioned between a device mounted on the top surface of the substrate and the surface of the heat sink. The heat transfer member includes a porous block of material having a heat conductive non-volatile liquid retained within the block of material by a surface tension. The heat transfer member is operative to transfer heat from the device to the heat sink.
Direct contact of the heat dissipating device, such as a heat sink or a thermal block, with the microprocessor is undesirable in many applications. Recently, some manufacturers have begun designing their microprocessors without an integral heat plate for being engaged by the heat dissipating device. As a result, the microprocessor can be easily damaged by stresses caused by direct contact with an object such as a heat sink or thermal block.
To permit effective heat transfer between the heat dissipating device and the heat generating component, such as between a heat sink and a microprocessor, a suitable thermal interface material is needed to ensure maximum surface-to-surface contact. Thermal pads, phase change materials and thermal grease represent the three most common types of thermal interface materials. Thermal greases and phase change materials typically have a thermal resistance approximately one-tenth that of thermal pads.
The superior thermal resistance of thermal greases and phase change materials is partially due to their being xe2x80x9cflowablexe2x80x9d materials. By flowable, it is meant that, above a specified temperature, they flow to conform to surface imperfections of the heat dissipating device and heat generating component. Another benefit of flowable materials is that their effectiveness is not adversely impacted by nominal misalignment between the heat generating component and the heat dissipating device. A major disadvantage of phase change material is that the phase change material does not release cleanly from the corresponding mating surface of the heat dissipating device and/or heat generating component when the heat dissipating body is detached from the heat generating component. Consequently, a residue remains on the mating surfaces of the heat dissipating body and heat generating component. Prior to reassembly, any residue must be cleaned from the surfaces.
Currently, elastomer pads are the preferred type of thermal interface material for portable computers. An elastomer pad is positioned between the heat generating component, such as the microprocessor, and the heat dissipating body, such as a heat spreading block. It is common for one side of the pad to be coated with an acrylic adhesive so that the pad may be attached to the heat spreader block without falling off prior to final assembly.
Acrylic adhesives have low thermal conductivity, adding significantly to the thermal resistance of the elastomeric pad. The microscopic gaps associated with roughness of the contact surface of the heat dissipating device are filled by the adhesive. Due to the low thermal conductivity of the pad, the effective thermal resistance between the heat generating component and the heat dissipating device is increased.
Accordingly, what is needed is a thermal interface member that provides a low thermal resistance at the mating surfaces of a heat dissipating body and a heat generating component and that cost-effectively facilitates replacement of the heat generating component.
One embodiment, accordingly, provides a thermal interface member including a first thermally conductive layer for being engaged with a surface of a heat dissipating device and a second thermally conductive layer for being engaged with a surface of a heat generating component. To this end, one embodiment provides a thermal interface member including a first thermally conductive layer and a second thermally conductive layer attached to a surface of the first thermally conductive layer. The first thermally conductive layer is resiliently compressible and the second thermally conductive layer is formed of a phase change material.
A principal advantage of this embodiment is that the heat transfer from a heat generating component to a heat dissipating device is significantly increased.